1. Field
The disclosure relates to loudspeakers for reproducing sound using an electrical signal.
2. Description of Related Art
The power of sound generated by a loudspeaker may be defined as the product between the square of the volume velocity of a medium (e.g., air) that moves due to vibration of a diaphragm and a radiation resistance caused by the shape of the diaphragm and the medium.
The volume velocity is proportional to the product of the area and dynamic range of the diaphragm. The volume velocity is determined by the dynamic range of the diaphragm when the fixed area of the diaphragm is considered. The radiation resistance corresponds to a real number of a radiation impedance of the diaphragm and is a physical quantity that directly contributes to acoustic power, which is effective power. The radiation resistance of a loudspeaker that includes a disc type driver installed on an infinite baffle decreases remarkably in a low-frequency band.
A woofer is designed to mainly reproduce sound in a low frequency band and is thus required to have a high volume velocity so as to reproduce sound at a desired level regardless of a low radiation resistance at a low frequency band. Thus, the woofer is required to have a much larger diaphragm area and dynamic range than a mid-range speaker or a tweeter. The volume of an enclosure should be increased to increase the area of the diaphragm of the woofer and maintain a low-frequency reproduction limit. Thus, it is difficult to manufacture the woofer of a slim type.
If increasing the volume of the enclosure is restricted, the dynamic range of the diaphragm may be increased to achieve a high volume velocity. When the dynamic range of the diaphragm is increased, a high volume velocity may be achieved, but the vibration energy increases and an electronic device in which the woofer is installed and peripheral structures may vibrate unnecessarily.